Sensitization of photographic emulsions



Patented June 1, 1943 OFFICE SEN SITIZATION OF PHO TOGRAPHIC EMULSIONSOskar Riester, Dessau-Haldeburg, Germany vested in the Alien PropertyCustodian No Drawing. Application February 17, 1942, Serial No. 431,265.In Germany August 8, 1940 My present invention of photographicemulsions. It is known to use for sensitizing silver halide emulsionsstyryl dyestuffs prepared by condensing nitrogenous heterocyclic basescontaining a reactive methyl or methylene group withdimethylaminobenzaldehydes. These styryl compounds are good bleachingout dyestuffs but inferior to other known cyanine dyestuffs, forinstance, trimethinecyanines as to intensity of sensitization. Myinvention is based on the observation that styryl dyestufis of thefollowing formula:

wherein A stands for groups of molecules necessary to complete a 5- or6-membered ring usual in cyanine dye art, for instance, indoline,thiazole, oxazole, quinoline, lepidine, benzimidazole.

- 'thiodiazole, isofurodiazole, selenazole, and these heterocyclicnuclei in turn may be substituted by alkyl, aryl, benzyl, phenylene,naphthylene or substituted phenyls and heterocyclic radicals or may becondensed with aromatic or heterocyclic rings;

R stands for alkyl, aralkyl, alkylene. or alkylenecarboxylic acid;

It: and R: stand for'hydroxyl or one of the substituents stands forhydroxyl and the other for hydrogen, alkyl, alkoxy', alkthio, carboxylor the like;

R: and R4 stand for halogen or one or the substituents stands forhalogen and the other for hydro n.

alkyl, alkoxy,- alkthio, carboxyl or the like;

Ra stands for hydrogen, alkyl, alkoxy, alkthio,

carboxyl or the like;

,8 stands for an acid radical, for instance, Cl, Br, I, 804, C104,-80am, SOaCaHs, and S0:.CeH4.CHs,

are valuable which can completely be removed from the photographiclayers already during the photographic process, that is duringdeveloping and l The dyestuifs, therefore, are useful especially incases it is of importance to obtain photographic layersfully undyedparticularly in the manufacture of photo-technical materials,photographic papers and photographic materials for scientific purposes.The dyestuffs of the present invention are very 890d sensltizers chiefly3 Claims.

relates to sensitization ortho-chromatic sensitizers,

for silver chloridebromide emulsions preferred for photographic papersand photo-technical materials. Moreover, the emulsions can be sensitizedfor a large range of the spectrum by the new dyestuffs in any way. Thusit is possible to obtain, for instance, panchromatic sensitizers and thesensitization curve of which falls away especially favorably and steeplytowards the long-wave lengths. x

The dyestuils of the present invention are prepared by reacting anitrogenous heterocyclic base carrying a reactive methyl or methylenegroup with a. halogenhydroxybenzaldehyde, iffnecessary in the presenceof a solvent.

The structure of these dyestuffs may be represented by the followingformula of the quinoid typ It is, however, more accurate to give thedyestuil's a betaine-like structure of the intramoiecular ionoid type:

The following examples are illustrative of my invention but they are notintended to be-limiting.

Example 1 A mixture oi 3 g. of 2-methylbenzoxazole ethyliodide, 3 g. of3.5-dibromo-4-hydroxy-benzaldehyde and 1 cc. of isoquinoline is meltedat C. for 10 minutes while stirring. The still hot melted mass is thendissolved in methanol and mixed with about 30 cc. of a 12% solution ofsodium acetate in methanol. A dyestufl of the following constitutioncrystallize o s n:

\C -CH -CHOOB Color of the methanolic solution: orange-yellow. Maximumsensitization: 525 m Example 2 4 g. of 2-methyl-4.5-diphenylthiazoleethyliodide and 3 g. of 3.5-dibromo-4-hydroxybenzaldehyde are dissolvedwhile boiling in a mixture of 20 cc. of pyridine and 20 cc. of alcohol.The

mass is then mixed with 2 cc. of piperidine and heated at 90 C. for 1hour. on cooling the following dyestufl crystallizes out:

Color of the methanolic solution: red-violet. Maximum sensitization: 580m Example 3 A mixture of 4.5 g. of Z-methyl-p-naphthothiazbleethyliodlde, 3 g. of 3.5 -dibromo-4-hy-1 dronbenzaidehyde, 20 cc. ofpyridine, '20 cc. of propanol, and 2 cc. of piperidine is boiled forhalf an hour. A dyestuif of the following formula crystallizes out:

Color of the methanolic solution: red-violet. Absorption maximum: 550 mColor of the pyridine solution: blue-violet. Absorption maximum: 590 mSensitization maximum: 590 mu.

. Example 4 y A mixture of 1.5 g. of 2-methyl-4-pheny1-isofurodiazoleand 1 cc. of dimethylsulfate is heated at 120C. for half an hour. Themass is then mixed with 2 g. of dibromohydroxybenzaldehyde and kept atthis temperature for half an hour. The dyestufl forms yellow crystalswhich dissolve in methanol containing some drops of pyridinewith a darkyellow color. The formula is as follows:

Absorption maximum: about 500 m Sensitization maximum: 520 m Example 5An orange-red dyestuff oi the following constitution is obtained bymeans of 2.5-dimethylthiodiazole in an analogous manner to that asdescribed in Example 4:

Color of the methanolic solution: orange-red.

7 Maximum sensitization: -545 m Example 6 A mixture of a g. ofquinaldine ethyliodide. 3 g. of dibromohydroxybenzaldehyde, and 10 cc.oi pyridine is boiled for 'half an hour. A violet- 'red dyestuf! of thefollowing constitution crystallizes out:

' n. crass-Q02:

lHl r Color of the solution: red-violet. Absorption maximum: about 550 mSensitization maximum: about 585111;.

Example 7 A mixture of equimolecuiar amounts of 2- methylthiazolinemethyliodide and 3.5-diiodo- 4-hydroxybenzaldehyde and some drops ofpyridine are melted together at C. for 1 hour. The mass thus prepared isthen dissolved in methanol. 0n addition of an ammonia solution of 1%strength a dyestufl of the following formula is obtained:

Ha Color of the methanolic solution: pure yellow. Maximum sensitization:515 m Example 8 5 g. of 2.5.6-trimethylbenzselenazole ethyliodide arecondensed with 5 s. of 3-bromo-4- hydroxybenzaldehyde in the presence of10 cc. of pyridine. One obtains a red dyestuif of the followingconstitution:

4 4 c--cn=cn-Qon 4 Color oi the methanolic Sensitization maximum:

Example 10 A mixture of 7 g. of 2-methyl-6-phenylbenzox- 8201a and 5.2g. of diethylsultate is heated at 120? C. in an oil bath for one hour. 9g. of 3.5-disolution: intensive red.

. bromo--hydroxybenzaldehyde and 3 cc. of pyridine are then addedthereto. The whole is heated at 120 C. for a further hour. Finally themelt is dissolved in 200 cc. of a methanolic solution or sodium acetateor 12.5%. On standing an orange-red dyestufl or the following formulacrystallizes out:

Absorption maximum 500 my.

I Sensitization maximum: 535 m Example 11 On replacing2-methyl-6-phenylbenzoxazole in Example 10 of2-methyl-6-chlorobenzoxazole an analogous dyestufl. likewise yielding anorangered solution and having the iollowing formula is Absorptionmaximum: 500 m Sensitization maximum: 530 m Example 12 1 g. of2-methyl-1-phenyl-benzimidazole and 5 cc. of dimethylsultate are heatedat 140 C. in an oil bath for one hour. 8 g. of the sodium salt oi.3.5-dibromo-4-hydroxybenzaldehyde (obtained by precipitating an aqueousalkaline solution 01' the dibromohydroxybenzaldehyde with a concentratedsolutionor sodium hydroxide in excess). 20 cc. oi pyridine and 5 cc. ofpiperidine are then added thereto and the whole is subsequently heatedat 110 C. for 6 hours. After acidifying the mass with diluted aceticacid the precipitated dyestufl' is sucked ofl', dissolved in methanoland slowly mixed with ether. Orange-red crystals dissolving in pyridinewith an orangered color are obtained. lowing formula:

Absorption maximum in pyridine: 525 mu.

' Color of the methanollc solution: yellow.

The dyestufi has the fol- Erample 13 A mixture of 5 g. of2-methylbenzthiazole-p propionyl bromide, 4 g. of 2-methyl-3.5-dibromo-4-hydroxybenzaldehyde'and 2 cc. of pyridine is heated at C. for half anhour. The melt is then rubbed together with propanol and th resultingdyestuil' sucked oil. It is of the following formula:

OOH

Color of the solution: carmine-red. Maximum sensitization: 555 m Example14 5 g. of 2-methylbenzthiazole-p-proprionylbromide and 5 g. of3-bromo-4-hydroxy-5-ethoxybenzaldehyde are condensed in the manner asdescribed in Example 13 to form a dyestufl of the followingconstitution:

(4 K)): Anna oon- Color 01' the solution: deep red. Maximumsensitization: 565 m Example 15 Maximum sensitization: about 547 m...

- I Example 16 When in Example 1.5 3.5-dibromoresorcylaldehyde is usedinstead of 3.5-dibromosalicylaldehyde, a dyestui! having the followingconstitution is produced:

The new sensitizers are incorporated into the silver'halide emulsions inthe usual way. In general about 20-50 kg. of emulsion.

I claim:

1. A photographic emulsion containing as the mg. of dyestufl. are usedfor 1 R: and R4 mean radicals from the class sensitizer a dyestui'f ofthe following general forconsisting of hydrogen and hydroxyl, at leastone of said radicals always being hydroxyl,

consisting ot'hydrogen, halogen, alkyl and alkoxy, at least one oi! saidradicals always being a halogen, a a Rs means a radical selected formthe class consisting oi hydrogen and alkyi'.

x means an anionic acid radical.

2. A photographic silver chloridebromide gelatin emulsion containing asthe sensitizer-a dyestui! as defined in claim 1.

3. A photographic paper comprising a silver chloridebromide gelatin,emulsion layer containing as the sensitizer a dyestui! as defined inclaim 05mm. 31mm.

